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Variovent versus polyfill

Doing some more thinking… The Scanspeak aperiodic “variovoents” versus polyfill.

I’m familiar w/ using aperiodic membranes but the “enclosure” is kept as small as possible and the assembly is mounted in a configuration that would otherwise be an IB if not for the aperiodic membrane. I think this results in a .7 Qt.

The Scanspeak vents seem to just be an add on to a sealed box w/o regard to keeping it’s “output” seperate from that of the woofers.

I don’t understand how the two are so similar but still different. Would a variovent be better utilized if it could be set up like the former example?

Re: Variovent versus polyfill

I wouldn't think it automatically results in a 0.7 Qt unless you are talking about a design someone else has already tested. You can measure the box parameters, and see what Qt results. Same for stuffing.

There is, however another use for aperiodic vents. George Short introduced the MAPD concept, a multichamber box with an aperiodic vent, for drivers with 0.6 - 0.7 Qts in free air. The final box Q is around 0.9. The ratio of the chamber volumes is about 1:3.

There is also an interesting design using Seas drivers that have a more conventional Qts of around 0.35. It uses a multichamber box but the ratio of the volumes is about 1:1.

The advantages to these designs is that for the upper bass, the speaker sees a small volume. Evidently it improves the upper bass clarity and power handeling. For lower bass, the speaker sees the full box volume but the aperiodic vent connecting the chambers helps reduce the Q at resonance. Again, to get it right, you should tune the vent by measuring the Qt.

Actually, I was going to bring this up in a day or so anyway. The second part of the article is due out sometime after the 31st (today).

There is also a classic AR type aperiodic vent design using the same driver you can read up on. I'm not as interested in the conventional aperiodic design because it is 18 dB/octave and while it controls the box Qt (boominess), I don't think you get the same bass out of a smaller box design. Nothing like a big box, baybee!!

> I’m familiar w/ using aperiodic membranes
> but the “enclosure” is kept as small as
> possible and the assembly is mounted in a
> configuration that would otherwise be an IB
> if not for the aperiodic membrane. I think
> this results in a .7 Qt.

> The Scanspeak vents seem to just be an add
> on to a sealed box w/o regard to keeping
> it’s “output” seperate from that of the
> woofers.

> I don’t understand how the two are so
> similar but still different. Would a
> variovent be better utilized if it could be
> set up like the former example?

Cool info... clarifications on my part

> I wouldn't think it automatically results in
> a 0.7 Qt unless you are talking about a
> design someone else has already tested. You
> can measure the box parameters, and see what
> Qt results. Same for stuffing.

The first "IBish" example was the .7 Qt. It was said to perform as if the driver was in an ideally sized sealed enclosure w/ a slight reduction in efficiency (from the air mass between the driver and aperiodic mambrane).

The ScanSpeak units seem to be used to lower the Qt from a higher value. The Mad catalog says you can decrease box size by 20%. I guess you could do the math to see what the Qt would be w/o the variovent.

My whole point was

> There is, however another use for aperiodic
> vents. George Short introduced the MAPD
> concept, a multichamber box with an
> aperiodic vent, for drivers with 0.6 - 0.7
> Qts in free air. The final box Q is around
> 0.9. The ratio of the chamber volumes is
> about 1:3.

> There is also an interesting design using
> Seas drivers that have a more conventional
> Qts of around 0.35. It uses a multichamber
> box but the ratio of the volumes is about
> 1:1.

> The advantages to these designs is that for
> the upper bass, the speaker sees a small
> volume. Evidently it improves the upper bass
> clarity and power handeling. For lower bass,
> the speaker sees the full box volume but the
> aperiodic vent connecting the chambers helps
> reduce the Q at resonance. Again, to get it
> right, you should tune the vent by measuring
> the Qt.

> Actually, I was going to bring this up in a
> day or so anyway. The second part of the
> article is due out sometime after the 31st
> (today).

> There is also a classic AR type aperiodic
> vent design using the same driver you can
> read up on. I'm not as interested in the
> conventional aperiodic design because it is
> 18 dB/octave and while it controls the box
> Qt (boominess), I don't think you get the
> same bass out of a smaller box design.
> Nothing like a big box, baybee!!

^^^Ignore above^^^ Read this one

My computer locked up in the middle of the above post, my apologies.

> I wouldn't think it automatically results in
> a 0.7 Qt unless you are talking about a
> design someone else has already tested. You
> can measure the box parameters, and see what
> Qt results. Same for stuffing.

The first "IBish" example was the .7 Qt. It was said to perform as if the driver was in an ideally sized sealed enclosure w/ a slight reduction in efficiency (from the air mass between the driver and aperiodic mambrane).
The ScanSpeak units seem to be used to lower the Qt from a higher value. The Mad catalog says you can decrease box size by 20%. I guess you could do the math to see what the Qt would be w/o the variovent.

The point of my post was to ask why are there there are two significantly different executions of components that are so similar

>... I'm not as interested in the
> conventional aperiodic design because it is
> 18 dB/octave and while it controls the box
> Qt (boominess), I don't think you get the
> same bass out of a smaller box design.
> Nothing like a big box, baybee!!

I wasn’t aware that they rolled off at that rate. In all my time playing with this with this enclosure design I have found time and time again that a big box is usually the best compromise. No free lucnh, except for polyfill (up to a certain point maybe)